Abstract More than 10% of adults in US are suffering from a variety of kidney diseases, which often start with trivial damages to the glomerular filtration barrier but are hard to detect in their early stages with conventional biomarkers. However, such damages can eventually lead to severe kidney dysfunctions without awareness until more than 60% of kidney function is lost. Thus, developing nanomedicines that allow early detection of glomerular dysfunction, a very beginning step in the kidney disease progression, is highly desired, which demands our comprehensive understanding of the glomerular filtration of engineered nanoparticles (NPs). While the glomerular filtration barrier is known a ?size cut-off? slit to retain engineered NPs or proteins larger than 6nm in the body and to rapidly excrete the smaller ones through the kidneys, we recently found that renal clearance of a class of sub-nm glutathione coated gold nanoparticles (sub-nm GS-AuNPs) was significantly slowed down by the glomeruli in the early elimination stage even though they eventually cleared out of the body through the urinary system. This surprising observation not only raises a fundamental question of how sub-nm engineered NPs interact with the glomerular barrier in vivo but potentially also opens up a new pathway for early detection of kidney diseases. The objective of this proposal is to fundamentally understand the glomerular filtration of sub- nm AuNPs and explore the feasibility of applying the newly discovered nano-bio interactions in early detection of glomerular injury. Three specific aims are proposed to accomplish the objective: Aim I is to investigate glomerular filtration of sub-nm AuNPs with well-defined size and surface chemistries. Aim II is to investigate glomerular filtration of sub-nm AuNPs with well-controlled glomerular endothelial glycocalyx (GEnG) degradation. Aim III is to apply NIR-emitting sub-nm AuNPs for early detection of GEnG injury in the preclinical settings. The success of the application will not only significantly advance our fundamental understanding of the glomerular filtration of engineered NPs but also lead to a new class of renal nanoprobes for early detection of GEnG injury at high sensitivity but low cost in the preclinical settings. Moreover, it will also lay down a foundation for future translation of renal nanomedicines for early diagnosis of kidney diseases.